1. Field
This disclosure relates generally to wireless communication devices, and more specifically to improving the dynamic range on the input of a receiver.
2. Background
Communication receivers receive both desirable and undesirable signals on their inputs. Signal selection filters for a receiver's “front-end”, such as preselect filters, have been designed for passing the desired signals relatively unfiltered and attenuating the undesired signals. The effectiveness of signal selection by a preselector is determined by the Q-value of a preselector's passband filter. Generally larger components in a passband filter may provide an adequate Q-value for providing the desired passband filtering. Conventionally, if the Q-value was inadequate, then larger, higher Q-value components were substituted until the preselector's passband filter provided adequate signal rejection.
As communication receivers became portable and mobile, various components in the receiver, including the receiver's front-end, have been integrated. Design tradeoffs exist between integration of receiver front-end components, such as passband filters, and the reduction in the effectiveness or quality of signal selection and rejection based upon the reduction of the Q-value of the filter components.
While it is desirable to further integrate the components of a receiver, attempts to further integrate bandpass filters results in inferior performance of the system. System requirements of narrow bandwidths, low distortion and the need for low-power consumption run counter to conventional integration approaches.
Further integration attempts have placed buffer components at the beginning of the receiver front-end resulting in a reduction of the dynamic range of the receiver front-end since buffer components include active devices which operate linearly only over a defined input signal dynamic range. Accordingly, when an RF input signal received at the receiver front-end includes undesired signals (jammer signals) of unpredictable magnitudes, then the active devices on a receiver's front-end may saturate, generate intermodulation signals and other non-linearities which may distort the desired input signal.
Larger off-chip circuit elements have allowed system requirements to be attained. However, larger-dimensioned circuit elements inhibit reductions in the overall dimensions of the device as well as contributes to increased device costs. Integration attempts may reduce the overall circuit component dimensions, however, such designs include shortcomings including difficulties achieving high operating frequencies with narrow bandwidths (i.e., high Q values) and a fundamental limitation on the dynamic range at high Q values.
Different receiver architectures (e.g., direct conversion or low IF designs) have attempted to overcome further integration shortcomings of passive components, however, the limitations on the dynamic range is prohibitive. For example, moving the channel select filtering to baseband results in amplifiers (e.g., Low Noise Amplifiers (LNAs)) and mixer circuits processing the entire RF spectrum including jamming (blocking) signals, resulting in the generation of further spurious responses and further desensitizing the receiver.
Improvements to poor dynamic range are possible by undesirably increasing the current consumption of circuit elements. For portable or mobile receivers, improving the dynamic range by increasing power consumption is undesirable and impractical. As stated, a bandpass filter includes passive elements (e.g., L/C, transmission lines, acoustic resonators) which in a bulk manufacturing quantities and integrated implementations results in very low Q-values for the bandpass filter. Accordingly, there is a need in the art for a receiver having a receiver front-end that exhibits high dynamic range on its inputs.